An example of coolant injection type nitrogen generating apparatuses currently in use is of a single rectification type, as shown in FIG. 3. This nitrogen generating apparatus performs the steps of: compressing air as a raw material in an air compressor 31; passing the compressed air through a drain separator 32 and a CFC cooler 33 into adsorption columns 34 to remove carbon dioxide and water from the compressed air; introducing the compressed air passed through the adsorption columns 34 through a supply pipe 35 into a main heat exchanger 36 to heat-exchange the compressed air with a refrigerant therein, thereby cooling the compressed air down to an ultra low temperature; introducing the compressed air cooled down to the ultra low temperature through an inlet pipe 37 into a rectification column 38 to cryogenically liquefy and separate the compressed air therein, thereby producing a product nitrogen gas; introducing the product nitrogen gas through a product nitrogen gas extraction pipe 39 into the above-mentioned main heat exchanger 36 to raise the temperature of the product nitrogen gas up to near room temperature; and feeding the product nitrogen gas into a main pipe 40. The above-mentioned rectification column 38 will be described in further detail. The rectification column 38 further cools the compressed air, cooled down to the ultra low temperature by the main heat exchanger 36, to liquefy part of the compressed air into liquid air 41, thereby storing the liquid air 41 in a bottom portion thereof, while storing only nitrogen in gaseous form in an upper portion thereof. The rectification column 38 includes a dephlegmator 42 incorporating a condenser 42a at its column top. Part of the nitrogen gas stored in the upper portion of the rectification column 38 is fed through a first reflux pipe 43a into the above-mentioned condenser 42a. The pressure in the above-mentioned dephlegmator 42 is lower than that in the rectification column 38. The stored liquid air (containing 50 to 70% N2; and 30 to 50% O2) 41 accumulated in the bottom portion of the rectification column 38 is fed through a feed pipe 44 with an expansion valve 44a into the dephlegmator 42, and is gasified to cool the internal temperature down to a temperature not greater than the boiling point of liquid nitrogen. This cooling liquefies the nitrogen gas fed into the condenser 42a, and the liquid nitrogen passes through a second reflux pipe 43b to flow down and be supplied to the upper portion of the rectification column 38. Liquid nitrogen is injected and supplied as a coolant from a liquid nitrogen tank (not shown) through an inlet pipe 45 into the upper portion of the rectification column 38. The liquid nitrogen flows down within the rectification column 38 to countercurrently contact and cool the compressed air raising from the bottom portion of the rectification column 38, thereby liquefying part of the compressed air. In this course, a high boiling point component in the compressed air is liquefied and stored in the bottom portion of the rectification column 38, and the nitrogen gas which is a low boiling point component is stored in the upper portion of the rectification column 38 (the boiling point of oxygen: approximately −183° C.; and the boiling point of nitrogen: approximately −196° C.). In FIG. 3, the reference numeral 46 designates a waste gas outlet pipe for feeding gasified liquid air (waste gas) within the dephlegmator 42 into the heat exchanger 36 to decrease the temperature of the compressed air passing therethrough, 47 designates a first release pipe for releasing the gasified liquid air passed through the heat exchanger 36 into the atmosphere, 48 designates a second release pipe for releasing a He gas in gaseous form (having a boiling point lower than that of the nitrogen gas) contained in the nitrogen gas into the atmosphere, and 49 designates a cold box for vacuum insulating the interior thereof.
Patent document 1: Japanese Patent Application Laid-Open No. 11-101576 (1999)